A conventional air conditioner including an inverter rotates a blower at a rotational speed corresponding to the air volume and air speed set by a user. A motor driving the blower is rotated either as a three-phase system that switches switching elements for three phases or as a two-phase system that fixes one of three phases to high or low and switches switching elements for two phases (refer to Patent Literature 1, for example).
Compared to the three-phase system, the two-phase system can reduce a power loss at the time of switching and also a power loss due to an overshoot. As for the waveform for driving the motor, on the other hand, the waveform of the three-phase system is smoother than the waveform of the two-phase system so that noise and vibration generated by the rotation of the motor are smaller in the three-phase system than in the two-phase system.